The present invention relates in general to the field of crosslinking protein, especially gelatin. The crosslinking of protein (and especially gelatin) is a well developed field in which many different means of crosslinking have been proposed.
The process of the present invention requires the use of a protein, a selected sugar (or sugars), a selected salt (or salts), at least a minimal amount of water, and a heating step. Never before the present invention has there been provided any process for crosslinking of protein with these ingredients. This particular combination of ingredients has been unexpectedly found to permit the crosslinking reaction to be performed at temperatures previously inoperable (i.e. too low) to obtain the desired degree of crosslinking with ingredients that are safe for both food and animal feed applications. This "low temperature advantage" is very important because it permits crosslinking to be performed in the presence of the many heat-sensitive materials (which of course have been present during the crosslinking process) without substantial thermal degradation. As a result, heat-sensitive ingredients can now be encapsulated within a gelatin which has been crosslinked, without any substantial degradation of the heat-sensitive ingredient during the crosslinking process. The process of the present invention offers a combination of crosslinking agents which, if making an edible product, are more desirable than previous crosslinking agents and processes in that the crosslinking temperature requirements are lower and/or the crosslinking agents are more desirable for purposes of making edible products.
The present invention is applicable to a wide range of arts, such as food sciences, photographic sciences, pharmaceuticals, etc, i.e. wherever protein crosslinking is utilized in combination with any additional chemical species which may be thermally sensitive, and in all situations in which it is advantageous to conserve energy. The invention is particularly useful in the vitamin arts, especially vitamin A, which undergoes thermal degradation at the temperatures previously required for obtaining substantial protein crosslinking with crosslinking agents which are considered both edible and safe for consumption. Thus the process of the present invention is particularly valuable for crosslinking protein (especially gelatin) in the presence of temperature-sensitive ingredients, such as vitamins, without substantial thermal degradation of the temperature sensitive ingredient.
The advantage is especially important with respect to producing protein-encapsulated vitamin A products. All of the ingredients utilized in the process are both edible and safe for consumption. Thus one is able to use the process of the present invention to obtain a vitamin A encapsulated in a crosslinked gelatin wherein the process is carried out at a temperature at which there is no substantial thermal degradation of the vitamin A.
U.S. Pat. No. 2,196,146 describes subject matter which is related to the present invention. The '146 patent relates to improved food products and process for making the same, and particularly to food products containing sugar and acid, such as those commonly known as gelatin desserts that generally are marketed in the form of a dry powder and usually comprise gelatin. Among the acids mentioned in the '146 patent are "fruit acids" (such as tartaric acid), and to the additional use of salts of organic acids such as acetates. The '146 patent repeatedly refers to the "setting" of the gelatin.
In contrast to the '146 patent, the present invention requires that the protein be "crosslinked". Crosslinking differs from "setting" in that crosslinking is irreversible whereas setting (also known as "gelation") is reversible. The process of setting involves the transformation of a solution to a gel. The addition of heat to the gel can then be used to melt the gel so that a solution is formed. In stark contrast, crosslinking involves an irreversible chemical reaction in that the addition of heat to the crosslinked protein will not result in transforming the crosslinked protein into a solution of the protein.
Another related patent of which applicants are aware is U.S. Pat. No. 4,500,453. This patent relates to crosslinked collagen-derived protein compositions having improved Bloom gel strength and increased viscosity. Furthermore, the '453 patent relates to improvement by crosslinking the protein with an aluminum salt of acetic acid selected from the group consisting of aluminum subacetate, aluminum triacetate and an alkali metal aluminum acetate double salt. The '453 patent requires the use of an aluminum salt, as can be seen from the comparative example therein (Example 2) which states that the substitution of a sodium salt for the aluminum salt is inoperable.
In contrast, the present invention differs from the '453 patent in that the process of the present invention requires the use of at least one of a group of sugars. If one were to alter the process of the present invention by carrying it out in the absence of at least one of these sugars, the required degree of crosslinking will not result. Note Comparative Example 2 herein, which proves that upon using, for example, calcium acetate as the salt, the process of the present invention is inoperable (no crosslinking occurs) in the absence of at least one of the group of sugars. In stark contrast, '453 patent nowhere mentions the use of any sugar, not to mention one or more of the group of sugars which are used in the process of the present invention.
U.S. Pat. No. 4,670,247 refers to a process for the preparation of fat-soluble vitamin active beadlet compositions which exhibit stability when exposed to the feed pelleting process. The process includes forming an aqueous emulsion of a fat-soluble vitamin-active material, gelatin, and a sugar, converting the emulsion to dry particulate form containing the non-aqueous constituents of the emulsion, and heat treating the resulting product to form water insoluble beadlets.
In contrast to the '247 patent, the process of the present invention requires the use of at least one of a group of salts. The '247 nowhere refers to either mandatory use of (or even optional use of) any salt whatsoever. Note Comparative Example 2 herein, which proves that even at a preferred temperature (75.degree. C. for the production of encapsulated vitamin A) for the process of the present invention, inoperability results in the absence of at least one of the group of salts specified.